Ethylene-alkyl acrylate copolymers and derivatives having improved melt-point temperatures

ABSTRACT

A composition is disclosed which comprises a copolymer of ethylene and alkyl acrylate having improved melt-point temperature and/or improved adhesiveness to polymeric substrates. A process for making these compositions is also disclosed. In addition, an ionomer made from the copolymer and a method for making the ionomer are disclosed.

This application is a divisional of application Ser. No. 08/233,180filed Apr. 26, 1994, now U.S. Pat. No. 5,571,878 which is acontinuation-in-part of application Ser. No. 07/764,861, filed Sep. 24,1991 now abd.

FIELD OF THE INVENTION

The present invention relates to copolymers of ethylene and an alkylacrylate, processes for preparing said copolymers, and compositions andfilms made from said copolymers.

BACKGROUND OF THE INVENTION

Copolymers of ethylene and acrylate esters and methods for theirmanufacture have been reported in the literature, such as in U.S. Pat.Nos. 2,200,429, 2,953,551 and 3,350,372. The '372 patent to Anspondiscloses an ethylene acrylate ester copolymer wherein the acrylateesters include, for example, methyl acrylate, 2-butyl acrylate,2-ethylhexyl acrylate, decyl acrylate, octadecyl acrylate and thecorresponding esters of methacrylic acid. The '372 patent states thatpreferred copolymers contain a maximum of 0.5 mole of acrylate ester permole of ethylene, i.e., 33 mole percent acrylate ester, and that thecopolymers ordinarily will contain at least 1 mole percent of theacrylate ester and preferably will contain 0.025-0.20 and moreespecially 0.05 to 0.15 mole of acrylate ester per mole of ethylene. Forethylene-methyl acrylate copolymer ("EMA"), 0.50 mole of acrylate permole of ethylene would be approximately 60 weight percent methylacrylate based on EMA copolymer, and 0.20 mole of acrylate per mole ofethylene would be approximately 38 weight percent methyl acrylate.

U.S. Pat. No. 3,756,996 to D. W. Pugh et al., which is herebyincorporated by reference in its entirety, discloses an apparatus andmethod for polymerizing ethylene and other monomers in a multi-zonedreactor system.

These ethylene-alkyl acrylate ("EAA") copolymers have been excluded fromsome markets because the melt-point temperature has been lower than whatthe market required of the EAA copolymer having a given amount of alkylacrylate. As more alkyl acrylate was incorporated into the copolymer tomake the copolymer more rubbery, the melt-point temperature of thecopolymer decreased sharply.

In addition, EAA copolymers have been excluded from other marketsbecause EAA copolymers have not had sufficient adhesive strength to,e.g., layers or films of other polymers to bind the EAA and otherpolymers strongly enough to prevent delamination. The present inventionprovides EAA copolymers with improved melt-point temperature and/orimproved adhesive strength, and a method for making these copolymers.

SUMMARY

This invention provides compositions comprising ethylene-alkyl acrylatecopolymers, which copolymers have higher melt-point temperatures for agiven percentage of alkyl acrylate in the copolymer than conventionalethylene-alkyl acrylate copolymers. In another embodiment, thisinvention provides compositions comprising ethylene-alkyl acrylatecopolymers, which copolymers have improved adhesive strength to otherpolymers such as polyester or polypropylene than conventional EAAcopolymers.

In particular, this invention discloses a composition comprising acopolymer of ethylene and alkyl acrylate, where the copolymer has amelt-point temperature of at least about 6 deg F. greater than areference copolymer which has the same amount and type of alkyl acrylateand ethylene and which is made in a multi-zone autoclave reactor withthe ratio of alkyl acrylate to ethylene in a reaction zone being aboutequal to the overall ethylene to alkyl acrylate ratio fed to themulti-zone autoclave reactor. Some of these copolymers also exhibit asubstantial increase in adhesive strength to other polymers overreference copolymers. Preferred embodiments include ethylene-methylacrylate and ethylene-butyl acrylate copolymers.

In another embodiment, this invention discloses a composition comprisingan ethylene-alkyl acrylate copolymer which has an adhesive strength topolyester or to polypropylene at least about 20% greater than areference copolymer which has the same amount and type of alkyl acrylateand ethylene and which is made in a multi-zone autoclave reactor withthe ratio of alkyl acrylate to ethylene in a reaction zone being aboutequal to the overall ethylene to alkyl acrylate ratio fed to themulti-zone autoclave reactor.

The invention also provides a process for the preparation ofethylene-alkyl acrylate copolymers comprising:

A. feeding overall an amount by weight, A, of alkyl acrylate and anamount by weight, E, of ethylene to a multi-zone autoclavepolymerization reactor;

B. introducing an effective amount of an initiator and at least aportion, E₁, of the total amount of ethylene into a first reaction zoneof the reactor;

C. concurrently introducing a portion, A₁, of alkyl acrylate to saidfirst reaction zone such that the ratio A₁ /E₁ is at least about 20%more than or is at least about 20% less than the ratio A/E for thereactor overall; and

D. feeding any remaining portions of initiator, ethylene and alkylacrylate to a subsequent is reaction zone or zones.

The invention also provides compositions comprising films or layers ofthe polymer of this invention which are contiguous to a second polymericfilm or layer such as polypropylene or polyester.

Among other factors, this invention is based on the discovery thatfeeding different ratios of ethylene to alkyl acrylate comonomer in atleast two reaction zones of a multi-zone autoclave reactor increases themelt-point temperature of the resultant EAA copolymer. This invention isalso based on the discovery that feeding different ratios of ethylene toalkyl acrylate comonomer in at least two reaction zones of a multi-zoneautoclave reactor can increase the adhesive strength of the resultantEAA copolymer. These advantages and others are further described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a preferred embodiment of the processof the present invention.

FIGS. 2 and 3 are correlation curves which give the relationship betweenthe weight percent of methyl acrylate ("MA") in EMA copolymer (FIG. 2)or weight percent of butyl acrylate ("BA") in EBA copolymer (FIG. 3),and the ratio of 8.6 μ to 6.8 μ absorbances, as measured by FourierTransform Infra-Red ("FT-IR") analysis.

FIG. 4 is a graph of adhesive strength of EMA copolymer as a function ofthe ratio of alkyl acrylate to ethylene in a first reaction zone (A₁/E₁) to total alkyl acrylate to total ethylene (A/E) for the reactor.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

According to one embodiment of the present invention, a high-pressureprocess is provided for producing ethylene-alkyl acrylate copolymers. Asused herein, the term "ethylene-alkyl acrylate copolymer" or "copolymerof ethylene and alkyl acrylate" refers to copolymers of ethylene andmethacrylic or acrylic esters of linear, branched or cyclic alcoholshaving 1-28 carbon atoms. Mixtures of these esters may also be used toprepare the copolymers of this invention. In addition, minor amounts ofother monomers may be used, provided they do not materially affect theproperties of the copolymers of this invention. The alkyl acrylatecomonomers are exemplified by methyl acrylate, ethyl acrylate, butylacrylate, and methyl methacrylate, and the ethylene-alkyl acrylatecopolymers are exemplified by ethylene-methyl acrylate copolymer("EMA"), ethylene-ethyl acrylate copolymer ("EEA"), ethylene-butylacrylate copolymer ("EBA"), and ethylene-methyl methacrylate copolymer.

The ethylene-alkyl acrylate copolymers of this invention typicallycontain about 5-50 wt % alkyl acrylate and about 95-50 wt % ethylene,preferably about 10-40 wt % alkyl acrylate and about 90-60 wt %ethylene, and more preferably about 15-40 wt % alkyl acrylate and about85-60 wt % ethylene. A particularly preferred copolymer contains about20 wt % alkyl acrylate and about 80 wt % ethylene. All weightpercentages are based on the combined weight of alkyl acrylate andethylene.

I. Process of Making the Copolymers of this Invention

As used herein, the following terms have the following meanings:

1. "A" is used herein to denote the total amount by weight of alkylacrylate fed to the reactor.

2. "A₁ " is used to denote the portion of the amount A which isintroduced into a first reaction zone in said reactor.

3. "E" is used to denote the total amount by weight ethylene fed to thereactor.

4. "E₁ " is used to denote the portion of the amount E which isintroduced into the first reaction zone.

One appropriate measure of these amounts is pounds (mass).

5. "A first reaction zone" refers to the first reaction zone in amulti-zone autoclave polymerization reactor in which 1) the weight ratioof alkyl acrylate to ethylene introduced into that zone is at least 10%greater than or at least 10% less than the weight ratio of the totalalkyl acrylate to total ethylene fed to the multi-zone autoclavepolymerization reactor; 2) at least 50% of the total alkyl acrylate A orat least 50% of the total ethylene E is present in said first reactionzone; and 3) an effective amount of initiator is introduced into saidfirst reaction zone. The amounts of alkyl acrylate and ethyleneintroduced into a zone are the amounts fed to that zone throughfeed-pipes and the amounts entering that zone from reaction zones otherthan said first reaction zone (if any), regardless of whether the alkylacrylate and ethylene were reacted in the other zones. Preferably, theamounts of alkyl acrylate and ethylene introduced into a zone are theamounts fed to that zone through feed-pipes and the amounts enteringthat zone from the reaction zone immediately upstream of said zone.

6. "Reaction zone" refers to an area within a single reaction vessel inwhich polymerization of the ethylene and/or alkyl acrylate takes place.Typically, the "reaction zone" is a portion of a single reaction vesselwhich is segregated from other areas of the same reaction vessel. Thissegregation can be accomplished by physical barriers (such as bafflesand the like), or other suitable means (such as the mixing patternswithin the reaction vessel). As used herein, the term "reaction zone"also includes areas in separate, multiple reaction vessels wherepolymerization occurs.

The process can best be understood in conjunction with FIG. 1 whichillustrates, in schematic form, a process for the manufacture andrecovery of ethylene-alkyl acrylate copolymers. Referring to FIG. 1,this process starts by feeding ethylene gas through line 2 via primarycompressor 5. The gas exits the compressor into line 6.

Line 6 is also the suction line for secondary compressor 10. Theethylene feed is compressed by secondary compressor 10 and dischargesinto line 12. The high-pressure feed is cooled in cooler 15. Theethylene feed stream is then fed to reactor 20.

Although multiple reactors may be used, in one preferred embodiment, theprocess uses a multi-zoned, high-pressure autoclave reactor. A 4-zonereaction system is preferred and is exemplified in FIG. 1, althoughadditional zones, such as six, or fewer zones, such as two zones, can beused.

Preferably, the ethylene is fed into the top of the reactor through line14 and into Zone 1. The reactor zones are numbered from top to bottom.Alkyl acrylate monomer is fed to the reactor through line 22 in anoverall amount by weight of A pounds, and is divided to feed selectedzones. In one embodiment, Zone 1 is fed A, pounds, and Zone 2 is fed(A-A₁) pounds.

In a continuous process like the four-zone autoclave reactor pictured inFIG. 1, the total feed of alkyl acrylate relative to the total ethylenefeed determines the alkyl acrylate content of the final copolymer. Acopolymer containing 20 wt % alkyl acrylate has a smaller total feedratio of alkyl acrylate to ethylene (A/E) than a copolymer containing 30wt % alkyl acrylate. To achieve the desired product, an overall A/E feedratio is chosen and generally maintained throughout a production run,although the ratio A/E can be varied over time to produce copolymerscontaining different weight percentages of alkyl acrylate.

As used herein, the term "conventional ethylene-alkyl acrylatecopolymers" refers to those ethylene-alkyl acrylate copolymers which aremade by dividing the ethylene monomer and alkyl acrylate monomer equallyamong the reactor zones to which monomers are fed. Thus, for aconventional ethylene-alkyl acrylate copolymer requiring overall that Aamount by weight of alkyl acrylate monomer be fed to the reactor and Eamount by weight of ethylene monomer be fed to the reactor, and for afour-zone reactor with two zones chosen for feeding reactants into thereactor, as illustrated in FIG. 1, the ratio of the amount, A₁, of alkylacrylate in a first reaction zone, to the amount, E₁, of ethylene insaid first reaction zone is equal to the ratio of the amount of alkylacrylate fed to a second reaction zone, A-A₁, to the amount of ethylenefed to a second reaction zone, E-E₁, (i.e., the ratio (A-A₁)/(E-E₁)),and is equal to the ratio of the overall amount of alkyl acrylate A tothe overall a mount of ethylene E (i.e., the ratio A/E).

It has quite surprisingly been discovered that the ratio of the amountby weight of alkyl acrylate monomer to the amount by weight of ethylenemonomer in a first reaction zone (A₁ /E₁) relative to the ratio of theoverall amount by weight of alkyl acrylate monomer to the overall amountby weight of ethylene monomer (A/E) is critical to obtain the improvedproperties of the ethylene-alkyl acrylate copolymer of this invention.It has unexpectedly been found that where the ratio A₁ /E₁ is at leastten percent greater than the overall ratio A/E or is at least tenpercent less than is the overall ratio A/E required to make theethylene-alkyl acrylate copolymer, the melt-point temperature of thecopolymer is significantly increased over conventional copolymers havingthe same alkyl acrylate content.

In one embodiment of the invention, the ratio of alkyl acrylate toethylene in a first reaction zone is at least ten percent less than theoverall ratio of alkyl acrylate to ethylene for the reactor. Preferably,the ratio is at least 25% less than and more preferably is 50% or even100% less than the overall ratio of alkyl acrylate to ethylene for thereactor. In one particularly preferred embodiment, the ratio of alkylacrylate to ethylene in a first reaction zone is zero. The ethylene, E,fed to the 4-zone reactor 20 of FIG. 1 is divided so that the amount ofethylene in Zone 1, fed through line 14, is between 0 and 100% of E,preferably is about 25% to 75% of E, and more preferably is 50% of E.About 75% to 0% of E, preferably 0% of E, is fed to Zone 2. Anyremaining portion of E, preferably 50% of E, is fed to Zone 3. Theamount of alkyl acrylate in Zone 1 is 0 to about 50% of A, andpreferably is 50% of A. An effective amount of initiator is alsopreferably introduced into Zone 1. About 50 to 0% of A, preferably 0%,is fed into Zone 2, which in this preferred embodiment is "a firstreaction zone" as defined above. Any remaining amount of alkyl acrylateand initiator is fed to the subsequent reaction zones, which in afurther preferred embodiment yields 50% of A being fed to Zone 3. Thetemperature in Zone 1 is preferably about 300° F. to 450° F., and morepreferably is about 325° F. to 425° F. The reaction zone pressurepreferably is about 10,000 to about 40,000 psig, more preferably about15,000 to about 35,000 psig, and most preferably is about 20,000 toabout 30,000 psig.

In another embodiment of the invention, the ratio of alkyl acrylate toethylene in a first reaction zone is at least ten percent greater thanthe overall ratio of alkyl acrylate to ethylene for the reactor.Preferably, the ratio is at least 25% greater and more preferably is 50%or even 100% greater than the overall ratio of alkyl acrylate toethylene for the reactor. In one particularly preferred embodiment, theratio is 300% greater than (i.e., 4 times) the overall ratio of alkylacrylate to ethylene for the reactor. Preferably, the ethylene, E, fedto the 4-zone reactor 20 of FIG. 1 is divided so that the amount ofethylene in Zone 1, fed through line 14, is about 25% to 75% of E,preferably is 25 to 50% of E, and more preferably is about 25% of E.

About 75% to 25%, and more preferably about half, of the ethylenemonomer is fed into Zone 2 through line 16. Any remaining portion of Eis fed to subsequent reaction zones, and preferably 25% of E is fed toZone 3. The amount of alkyl acrylate in Zone 1 is about 100% to 25% ofA, and preferably is 100% of A (in this preferred case where all of thealkyl acrylate is fed to Zone 1, Zone 1 is "a first reaction zone" asdefined above). The amount of alkyl acrylate fed to Zone 2 is 0% toabout 75% of A, and preferably is 0%. Any remaining alkyl acrylate isfed to subsequent reaction zones, and preferably is fed to Zone 3.

It has also unexpectedly been found that where the ratio A₁ /E₁ is atleast ten percent greater than the overall ratio A/E, the adhesion of afilm of the copolymer to a film of a substrate such as another polymerincreases. For the 4-zone autoclave reactor of FIG. 1, the preferredprocess described in the paragraph immediately above providesethylene-alkyl acrylate copolymers having substantially increasedadhesion to polyester or polypropylene films, including orientedpolyester or oriented polypropylene films.

A free radical initiator is preferably used to catalyze thepolymerization. The initiator can be added into any zones wherepolymerization is desired. The initiator preferably is fed into at leastthe first reaction zone in a sufficient amount and rate whereby thetemperature of the liquid phase in the reaction zone is controlled inthe range specified above. For example, in the process of FIG. 1, theinitiator can be added into Zone 1 or to both Zone 1 and Zone 2 throughline 18. Optionally, the initiator can be added to Zones 3 and 4 aswell.

The initiator may be added to the reaction zone(s) in any suitablemanner. Generally, it is dissolved in a suitable solvent, typically ahydrocarbon, and injected into the zone(s). Normally, the initiator andalkyl acrylate are simultaneously injected into the reaction zone(s),though this is not essential. In a preferred embodiment, the initiatorand alkyl acrylate are simultaneously injected into the reaction zonevia concentric tubes, one carrying the initiator and the other carryingthe alkyl acrylate.

Examples of initiators useful in the practice of this invention include,but are not limited to, peroxides such as lauroyl peroxide, t-butylperbenzoate, t-butyl peroxypivalate and di-t-butyl peroxide. A preferredinitiator is t-butyl peroxypivalate. Typically, the initiator isdissolved in a liquid hydrocarbon such as is hexane or mineral oil.

In preparing the ethylene-alkyl acrylate copolymers of this invention,it is desirable to add an oxygen scavenging compound to the reactionmixture. Phenolic compounds are useful in this regard. These phenoliccompounds include 2,6-di-t-butyl-4-methylphenol (BHT) and2,6-di-t-butyl-4-ethylphenol (BHEB). These compounds are well known inthe art; see U.S. Pat. No. 3,941,747, issued Mar. 2, 1976 to Roth etal., which is incorporated herein by reference. A preferred compound isBHEB. The addition of the oxygen scavenging compound is at a rate suchthat the concentration of the compound is preferably 0.01 to 0.5, morepreferably 0.05 to 0.10 wt %, of the total copolymer produced.

The reaction mixture is agitated within said first reaction zone toproduce both radial and longitudinal mixing. Preferably a substantiallyuniform reaction temperature is maintained.

The reaction mixture proceeds from the first reaction zone into a secondreaction zone. The reaction mixture in the second zone preferably isagitated to produce good radial and longitudinal mixing. In onepreferred embodiment, the remaining alkyl acrylate monomer, ethylene andadditional free radical initiator are introduced into the secondreaction zone. Also preferably, the three components are addedseparately and concurrently into the second reaction is zone. Theinitiator is fed into the second reaction zone in a sufficient amountand rate whereby the temperature of the liquid phase in the finalreaction zone is controlled to about 350° F. to 450° F., more preferablyto about 350° F. to 425° F., and most preferably 375° F. to 425° F.

Preferably, there are one or more reaction zones after the secondreaction zone which are used to further polymerize the ethylene andalkyl acrylate monomers. Referring to FIG. 1, the reaction mixture isremoved from the end of Zone 2 (the second reaction zone, in this case)and introduced into two additional reaction zones, where the mixture isagitated to produce both radial and end-to-end mixing.

The reaction mixture is removed from the final reaction zone. Theproduct, which contains ethylene-alkyl acrylate copolymer, unreactedethylene and other impurities, leaves reactor 20 of FIG. 1 and istransferred, via pressure differential, through line 24 to separator 30.In separator 30, the molten copolymer is separated from the unreactedethylene, and the ethylene is recycled back, via line 4, to the suctionof secondary compressor 10. A voluntary purge is removed from therecycle, via line 26, in a sufficient amount to obtain the desiredpurity of the ethylene returning to secondary compressor 10. Impuritiesthat need to be removed include telogens, which reduce the molecularweight of the polymer, as well as other process compounds affecting thepurity of the recycled ethylene.

The molten polymer leaves separator 30 and is transferred, via line 28,to hopper 35. Transfer is accomplished by a pressure differentialbetween separator 30 and hopper 35.

In the preparation of polymers, as in bulk and solution polymerizationor by other standard methods, considerable amounts of startingmaterials, such as unreacted monomer or solvent, remain admixed orentrained in the polymer product. This contamination of polymer isundesirable because of well known adverse effects on polymer properties.Since the contaminants in most cases are volatile relative to theirpolymeric hosts, they are removed from the condensed phase (polymer) byevaporation into a contiguous gas phase. Such separation processes arecommonly referred to as devolatilization ("DV"). The process ofdevolatilization in DV zone 55 of FIG. 1 is preferably used to preventthese volatile components from contaminating the copolymer product. Thisis done before the product is fed to gear pump and pelletizer 40.

In one embodiment of the invention, devolatilization is accomplished byventing the volatile components prior to extrusion. However,devolatilization is well known in the art, and other methods may be usedor adapted. See "Encyclopedia of Polymer Science & Engineering", 2d Ed.,Vol. 4, pp. 745-51 (1986), which is incorporated herein by reference.

The ethylene-alkyl acrylate copolymers of the present invention aretypically produced in the form of pellets. If the surface of thepelletized ethylene-alkyl acrylate copolymer tends to be sticky, it ispreferable to coat or dust the pellets to prevent agglomeration. Coatingagents selected from the group consisting of silicas, talc, and powderedpolyolefins are used. Preferably, talc or powdered polyethylene is used.Preferably, integral to the coating step, the pellets are classifiedaccording to their size for packaging.

II. Improved Properties of the Copolymers and Their Uses

There are several improved properties of the copolymers of thisinvention that are particularly advantageous. These include an increasedmelt-point temperature and enhanced adhesion to substrates.

A. Higher Melt-Point Temperatures

The copolymers of this invention have surprisingly higher melt-pointtemperatures than ethylene-alkyl acrylate copolymers prepared usingconventional methods. As can be seen from the data of Table 1, themelt-point temperatures of the ethylene-alkyl acrylate copolymers of thepresent invention are at least about 6° F. higher than the melt-pointtemperatures of conventional ethylene-alkyl acrylate copolymers having acorresponding alkyl acrylate content. Generally, these melt-pointtemperature differences increase as the alkyl acrylate content of thecopolymers increases.

The lowest melt-point temperature for the ethylene-methyl acrylatecopolymers of this invention can be expressed in terms of the alkylacrylate content of the copolymer, denoted by "Y" where Y is greaterthan ten:

    temperature (deg F.)=248-3.1Y.                             Eq. 1

For EBA copolymer of this invention, the relationship of the lowestmelt-point temperature to BA content, denoted by "Z" where Z is greaterthan 10, is:

    temperature (deg F.)=240-2.3Z.                             Eq. 2

Preferably, Y and Z are at least about 15, and more preferably are atleast about 20.

Higher melt-point temperatures are an advantage in applications wherehigher end-use temperatures are required or where the product ispotentially subject to high temperatures. For example, EMA copolymer andEBA copolymer are used to fabricate gaskets and plastic valvecomponents. These articles may be subject to high temperatures duringshipping, storage or use. Less shape distortion would occur at thesetemperatures using the high-melt-point copolymers of this invention.Indeed, the higher melt-point products of this invention provide for abroader range of useful operating temperatures and thereby increase thenumber of potential applications for ethylene-alkyl acrylate copolymers.EMA and EBA copolymers are also used as films or layers in single-layeror multi-layer constructions, such as food wrap.

When making films comprising the copolymer of this invention, it isoften desirable to add anti-block and slip additives to aid withprocessing and handling of the films. Slip additives are preferablyadded in the range of about 0.1 to about 0.5 wt % of the polymer. Usefulslip additives include high molecular weight paraffinic amides, such asstearamide, oleamide and erucamide. Anti-block additives are preferablyadded in the range of about 0.3 to about 1.5 wt % of the polymer. Theyhave very small particle size and are preferably natural or syntheticsilicas, diatomaceous earths and talc.

B. Improved Adhesive Strength

In one preferred embodiment, copolymers of this invention are quiteuseful as adhesives, especially in extrudable film applications such asmulti-layer extrusions. Such applications could include, for example,automotive door panels. Here, the adhesive must be stable to atemperature of about 180° F. to withstand the heat of a car interior ona hot day.

In one embodiment of this invention, the adhesive strength of thecopolymer remains substantially the same as a conventional copolymer,even though the melt-point temperature has increased substantially.Typically, the adhesive strength of this type of copolymer increasesless than 20%, and preferably less than 10%, over the adhesive strengthof a conventional copolymer. The melt-point temperature increases by atleast about 6° F. over a conventional copolymer having about the samemelt-index.

In another embodiment of this invention, both the melt-point temperatureand the adhesive strength of the copolymer increase substantially. Inthis embodiment, the melt-point temperature increases by at least 6° F.and the adhesive strength increases by at least about 20%, preferably byabout 50%, and more preferably by about 100%, over a conventionalcopolymer.

In a further embodiment of this invention, the adhesive strength of thecopolymer increases substantially, while the melt-point temperatureremains substantially the same as a conventional copolymer. In thisembodiment, the melt-point temperature of the copolymer is less than 6°F. above the melt-point of a conventional copolymer, but the adhesivestrength increases by at least about 20%, preferably by about 50%, andmore preferably by about 100%, over a conventional copolymer.

C. Improved Polymer Blends

The ethylene-alkyl acrylate copolymers of the present invention areuseful in preparing polymer blends which, in turn, are useful in makingfilms. For example, the ethylene-alkyl acrylate copolymers of thisinvention can be blended with a polyolefin such as polyethylene by meltblending techniques to produce a composition which is useful inpreparing films. As used herein, the term "polyolefin" refers tohomopolymers and copolymers of alpha-olefins having from 2 to about 8carbon atoms, such as high density polyethylene, low densitypolyethylene, linear low density polyethylene, and polypropylene.Optical properties, melt-point temperature, and adhesiveness of theseblends often improve as a result of blending copolymer of this inventionwith other polymers.

The high melt-point copolymers of this invention are particularly usefulin blends with other polymeric materials. Here, the melt-point of theethylene-alkyl acrylate copolymer can be chosen to better match theother blend component(s) and the requirements of the desiredapplication. Again, these blends could be used in applications requiringhigher temperatures.

In sum, the improved melt-point temperature and/or adhesive strengthallows use of the copolymers of this invention where previousethylene-alkyl acrylate copolymers could not be used due to their lowermelt-point temperatures and/or adhesive strength.

III. Derivatives of the Copolymers of this Invention

Derivatives of the copolymers of this invention as described below alsopossess improved properties, such as higher melt-point temperatureand/or higher adhesion. This will permit use of these derivatives in awider range of applications; for example, derivatives may be used inmulti-layer extrusions or elsewhere where adhesion is desired, e.g.,where gas barrier films are adhered to rigid plastics or other materialswhich are to be used in higher temperature applications. A variety ofderivatives may be produced using methods well known in the art.

The polymers of the present invention can be partially or totallysaponified to produce ionomers by reacting an ethylene-alkyl acrylatecopolymer of this invention and an aqueous solution of an inorganicalkali metal base at a temperature sufficient for saponification tooccur.

Among other factors, the present invention is based on the discoverythat (1) ionomers made from the ethylene-alkyl acrylate copolymers ofthis invention have higher melt-points than ionomers made fromconventional ethylene-alkyl acrylate copolymers, (2) the ionomers ofthis invention have higher melt strength than ionomers made fromconventional ethylene-alkyl acrylate copolymers which results in betterprocessability at higher temperatures, e.g., they are stronger whenmolten, (3) the ionomers of this invention provide good adhesion tometal, e.g., aluminum, foils, and (3) films made from ionomers of thisinvention have improved clarity. In addition, when the ionomers of thisinvention and ionomers made from conventional ethylene-alkyl acrylatecopolymers are formed into strands and stretched, the ionomers of thisinvention stay nearly transparent, do not whiten and have a highertensile strength than the unstretched strand, whereas the stretchedstrands made from conventional ionomers turn white and "foamy" andbecome weaker.

Ethylene-sodium acrylate-methyl acrylate terpolymers (ionomers) madefrom conventional, ethylene-methyl acrylate copolymers having randomacrylate unit sequence distribution are heterogeneous due to the limitedcapability of the randomly dispersed methyl acrylate groups tohomogenize the sodium acrylate aggregates by solvation. Theseconventional terpolymers have exhibited two-phase morphology in which asodium-rich phase is dispersed in a sodium-poor matrix. The aggregatesare usually larger than one micron in diameter.

As a result, films fabricated from these conventional terpolymers havepoor optical properties, such as high haze and low gloss values. Theheterogeneity also causes anisotropy in fabricated articles in the sensethat films or extrudates turn opaque as they are stretched. The inherentstructure and morphology of these conventional terpolymers with randomlydistributed acrylate groups result in low values of the ultimatelyachievable performance properties.

On the other hand, ethylene-sodium acrylate-methyl acrylate terpolymers(ionomers) made from the ethylene-methyl acrylate copolymers of thisinvention have a unique acrylate comonomer sequence distribution incomparison with the conventional terpolymers. A higher percentage ofacrylate groups in the ionomers of this invention is distributed inblocks, i.e., methyl acrylate groups are bonded to each other. Thesolubilization of the sodium acrylate groups in the terpolymers of thisinvention is thus provided by the localized high polarity region inwhich one or more of the blocks of methyl acrylate are located. Thistype of structural character produces local regions of high polaritywhich efficiently solubilize the ionic clusters of sodium acrylate toform much smaller clusters which can not even be observed by ScanningElectron Microscopy (SEM).

The smaller size of the ionic clusters of the ionomers of the presentinvention causes the polymers to have a homogeneous, one-phasemorphology. This dispersion of the smaller size but larger number ofionic groups significantly increases the interfacial area between theionic clusters and the matrix versus the conventional terpolymers. This,n turn, produces polymers with lower melt flow rates.

As used herein, the term "inorganic alkali metal base" refers to basiccompounds which contain a metal from Group I of the Periodic Table as acation, and an inorganic anion. For the purposes of this invention, acarbonate anion is considered to be inorganic. Examples of the inorganicalkali metal bases useful in preparing saponified products include, butare not limited to, alkali metal hydroxides (such as NaOH, KOH andLiOH), alkali metal oxides (such as Na₂ O, K₂ O and Li₂ O) and alkalimetal carbonates (such as Na₂ CO₃, K₂ CO₃ and Li₂ CO₃). A preferredmetal base is NaOH.

In a preferred embodiment, the saponification reaction is carried out atrelatively high temperatures so that the ethylene-alkyl acrylatecopolymer will undergo a phase change. As used herein, the phrase"undergo a phase change" means that the ethylene-alkyl acrylatecopolymer (which is a solid at room temperature) has been heated atleast to the point where it is readily deformed. Generally, this willmean that the copolymer has been heated until it is converted to amolten or fluid state. In general, the reaction temperature may be fromabout 180° C. to about 300° C. Higher reaction temperatures may be used,though discoloration and/or degradation of the polymer may occur.Likewise, lower temperatures may be used, but these lower temperaturesmay require excessively long reaction times. Preferably, the reactiontemperature will be from about 200° C. to about 280° C.

This preferred saponification process can be conducted in any suitablemixing device such as a Brabender Plasticorder, a roll mill, a single ormultiple screw extruder or any other of the well known mechanical mixingequipment normally used in the mixing, compounding, processing orfabrication of low or high molecular weight thermoplastic, elastomericor thermosetting polymers or mixtures thereof. An extruder having one ormore ports is a particularly desirable reaction vessel, although it isby no means necessary insofar as the saponification reaction can be donein other reaction vessels. Suitable extruders are described in U.S. Pat.No. 4,857,600, issued Aug. 15, 1989 to Gross et al., which isincorporated herein by reference. The saponification reaction preferablyoccurs in a reactive extruder, where the ethylene-alkyl acrylatecopolymer can be injected molten or be melted in situ, and where thealkali metal base can be added into the first and/or subsequent reactionzones.

Preferably, the residence time for the reaction mixture in an extruderwill generally be about 0.1 to about 30 minutes, the particularresidence time being chosen so that the desired level of saponificationis achieved. Of course, the residence time may vary depending upon theparticular reaction conditions employed, the reaction temperature,throughput, extruder RPM, and the like.

The products of the reaction are an alkanol (the alkyl group of whichcomes from the alkyl acrylate comonomer) and a terpolymer of ethylene,alkyl acrylate, and an alkali metal salt of acrylic acid, assuming, thatis, that less than 100% of the alkyl acrylate is saponified. The degreeof saponification can be varied, and is controlled by the amount ofinorganic alkali metal base used and reaction conditions. Whileessentially all of the acrylate groups on the copolymer can besaponified, this generally results in a highly cross-linked, extremelytough material which may be difficult to process. Generally, therefore,about 2% to about 90%, preferably about 5% to about 70%, more preferablyabout 10% to about 60% of the acrylate groups on the copolymer aresaponified. The resulting terpolymer has some remaining ester groups,which desirably function as a plasticizer.

After reaction completion, any water and by-product alkanol remaining inthe reaction product can be removed, for example, by devolatilization.Also, any unreacted inorganic alkali metal base remaining in thereaction product will usually be neutralized.

EXAMPLES

The following examples illustrate particular embodiments of theinvention and do not limit the scope of the invention disclosed above.

Example 1 EMA Copolymer Preparation Having 20 Weight Percent MethylAcrylate

A conventional EMA copolymer and EMA copolymer of this invention wereprepared in a 4-zone autoclave reactor, as illustrated in FIG. 1. Theethylene and methyl acrylate ("MA") were fed into the reactor so thatvarying proportions of MA were fed into Zone 1.

Ethylene was charged to the reactor at a rate of 12,000 lbs./hr., withthe percentages fed to each zone being listed in Table 1 below. Theethylene charged to the reactor had a purity of about 99.9% andcontained less than 10 ppm of oxygen.

MA was fed to the reactor at an overall rate of about 370 lb./min. Thepercent of MA injected into the reactor zones was varied as shown inTable 1. The ratio of the quantity A₁ /E₁ to the quantity A/E is alsoshown in Table 1 below for the experimental feed splits. The copolymersof this invention were produced when the ratio A₁ /E₁ was at least about10% greater than or at least about 10% less than the overall ratio forthe reactor, A/E.

The MA contained about 50 ppm methyl ethyl hydroquinone, apolymerization inhibitor, and had an oxygen content of less than 20 ppm.The initiator, tertiary butyl peroxy pivalate, was dissolved in ahydrocarbon carrier and introduced into the first and second reactionzones at a rate of 4.8 lbs./hr., which is 380 ppm based upon the weightof monomers charged. The polymerization was conducted at pressures andtemperatures typically used to prepare ethylene-alkyl acrylatecopolymers. Good mixing was provided in each zone via internalagitation. Butylated hydroxyethylbenzene (BHEB) was added at a rate tomaintain 650 ppm based on polymer produced.

The reaction mixture was discharged from the reactor as molten polymer.Unreacted ethylene was separated and recycled. Using a gear pump, theEMA copolymer was extruded through a die having a series of 1/8" holesinto a water bath at 90° F. The resulting strands were pelletized anddried. The ethylene-methyl acrylate copolymer that was obtainedcontained approximately 20-23 wt % methyl acrylate. Properties of thecopolymers so obtained are summarized in Table 1 below.

Melt-point temperatures for the copolymers were measured by using aPerkin-Elmer Differential Scanning Calorimeter DSC-7 and by utilizingstandard methods well known in the art.

                                      TABLE 1                                     __________________________________________________________________________                                             % of                                     Wt. % and                            Methyl                                                                             Ratio of                            Type of                              Acrylate                                                                           A.sub.1 /E.sub.1 to                 Comonomer                                                                           Melt-                                                                             Melt-                                                                            % MA/%                                                                              % MA/%                                                                              % MA/%                                                                              % MA/%                                                                              Introduced                                                                         A/E in a                            in    point                                                                             index                                                                            ETHYLENE                                                                            ETHYLENE                                                                            ETHYLENE                                                                            ETHYLENE                                                                            into a First                                                                       first                           Run Ethylene                                                                            Temp.                                                                             (g/10                                                                            FED TO                                                                              FED TO                                                                              FED TO                                                                              FED TO                                                                              Reaction                                                                           reaction                        Number                                                                            Copolymer.sup.2                                                                     °F.                                                                        min.)                                                                            ZONE 1.sup.4                                                                        ZONE 2.sup.4                                                                        ZONE 3.sup.4                                                                        ZONE 4.sup.4                                                                        Zone zone                            __________________________________________________________________________    A.sup.1                                                                           22.5                                                                             MA 181 6.2                                                                              50/50 50/50 0/0   0/0   50   1.0                             B.sup.1                                                                           20.7                                                                             MA 185 1.9                                                                              50/50 50/50 0/0   0/0   50   1.0                             C   21.3                                                                             MA 182 5.6                                                                              25/50 25/50 50/0  0/0   25   0.5                             1   21.5                                                                             MA 188 5.5                                                                               0/50 50/50 50/0  0/0   0    0.0                             2   21.3                                                                             MA 191 5.8                                                                              50/50  0/50 50/0  0/0    50.sup.3                                                                          0.5                             3   22 MA 198 6.7                                                                              100/50                                                                               0/50 0/0   0/0   100  2.0                             4   20.6                                                                             MA 201 2.0                                                                              100/50                                                                               0/50 0/0   0/0   100  2.0                             5   20.3                                                                             MA 201 1.7                                                                              50/25 50/50  0/25 0/0   50   2.0                             6   22 MA 207 6.6                                                                              100/25                                                                               0/50  0/25 0/0   100  4.0                             D.sup.1                                                                           21 BA 190 -- 50/50 50/50 0/0   0/0   50   1.0                             7   22 BA 203 -- 100/50                                                                               0/50 0/0   0/0   100  2.0                             __________________________________________________________________________     .sup.1 Experiments A and B are conventional copolymers and are comparativ     experiments.                                                                  .sup.2 MA--methyl acrylate; BA--butyl acrylate.                               .sup.3 Zone 2 is a first reaction zone for this example.                      .sup.4 Percentages of respective feedrates of MA and ethylene fed to each     zone. Melt index was determined using ASTM Method D1238 @ 190° C.      using a 2.16 kg mass.                                                    

Example 2 Measuring the Alkyl Acrylate Content of the Copolymer

The alkyl acrylate content of the copolymers made in Example 1 wasmeasured by Fourier Transform Infra-Red spectroscopy (FT-IR). A sampleof devolatilized copolymer was pressed into a thin film and scanned inthe infrared region. The procedure used a Nicolet Model No. 510 FT-IRscanning infrared spectrophotometer. Seven to ten pellets (about 1/2gram) or an appropriately-sized molded article were placed between twopieces of Mylar, approximately 4.75 mils thick. A 1" wide strip of Mylarwas placed on top of the Mylar release sheet, so that it would cover thecenter of the sample. The Mylar "sandwich" was placed between 8"×8"platens of a 50,000 psig capacity Pasadena Hydraulics heated hydraulicpress. The press was brought up to contact pressure (<1000 lbs.) at atemperature of about 350° F. The copolymer was allowed to melt (about 45sec.). The press was then brought to 40,000 lbs. pressure, which wasmaintained for 10 sec. The pressure was released, and the samples werewithdrawn. The sample was placed between two steel plates and allowed tocool (2 minutes).

As specified below, the areas of interest were measured, and a ratio ofabsorbance values was obtained. The weight percent of methyl acrylatewas determined from FIG. 2, which is a correlation chart for absorbanceratio versus weight percent methyl acrylate in EMA copolymer. The weightpercent of butyl acrylate was determined from FIG. 3, which is acorrelation chart for absorbance ratio versus weight percent butylacrylate in EBA copolymer.

FIGS. 2 and 3 were derived from samples of conventional EMA copolymerand EBA copolymer which were assigned nominal values of MA or BAcontent, based upon information from the supplier of the samples. Forother ethylene-alkyl acrylate copolymers, such standard techniques asNMR or elemental analysis can be used to develop correlation graphssimilar to those of FIGS. 2 and 3.

The Mylar was carefully removed from the pressed sample. The center areaof the pressed sample was mounted to a metal holder. It is important notto stretch the sample, since stretching can cause erroneous results.

A. Determination of Weight % MA in EMA Copolymer

The mounted sample was placed in the infrared beam and scanned from 4000to 400 cm⁻¹. The area from 1518.75-1407.42 cm⁻¹ was integrated andlabelled as the 6.8 μ absorbance. The area from 1323.93-1047.61 cm⁻¹ wasintegrated and labeled as the 8.6 μ absorbance. The ratio of the 8.6 μabsorbance to the 6.8 μ absorbance was used to determine the MA contentof the copolymers. Percent methyl acrylate was read directly from FIG.2, which defines the relationship between the ratio of the 8.6 μabsorbance to the 6.8 μ absorbance and the weight percent methylacrylate in EMA copolymer.

B. Determination of Weight % BA in EBA Copolymer

The sample was formed and mounted as described above, and placed in theinfrared beam and scanned from 4000 to 400 cm⁻¹. The area from 1501-1409cm⁻¹ was integrated and labelled as the 6.8 μ absorbance. The area from1225-1046 cm⁻¹ was integrated and labeled as the 8.6 μ absorbance.

The ratio of the 8.6 μ absorbance to the 6.8 μ absorbance was used todetermine the BA content of the copolymers. Percent butyl acrylate wasread directly from FIG. 3, which defines the relationship between theratio of the 8.6 μ absorbance to the 6.8 μ absorbance and the weightpercent butyl acrylate in EBA copolymer.

Example 3 Adhesion of Copolymers of this Invention to Polyester

A comparative three-layer cast film consisting of a 2-mil layer ofpolyester (Eastman 7352), a 1-mil layer of EMA copolymer prepared by theconventional process and having a melt-index (MI) of about 2(Comparative Run B of Table 1), and a second 2-mil layer of saidpolyester, respectively, were prepared on a Randcastle Mini-extruder.Three-layer cast films of this invention were prepared by substituting a2 MI ethylene-methyl acrylate copolymer made by the process of thisinvention for the EMA copolymer made by the conventional process.

Adhesion of the EMA copolymer layer to a polyester layer was measuredusing a Rheometrics RDA-700 analyzer and the method described in TAPPIUniform Method 541, "Adhesion to Non-Porous Flexible Substrates," whichis incorporated herein by reference in its entirety. The adhesion forthe comparative film and for film of this invention are summarized inTable 2, and this data is shown graphically in FIG. 4.

                  TABLE 2                                                         ______________________________________                                              EMA COPOLYMER    WT. % MA IN                                                  PREPARED BY METHOD                                                                             ETHYLENE   ADHESION                                    RUN   OF RUN NO. OF TABLE 1                                                                          COPOLYMER  (gm/in.)                                    ______________________________________                                        E.sup.5                                                                             COMPARATIVE RUN B                                                                              20.7       360                                          8    3                20.6       860                                          9    4                20.3       1,000                                       10    5                22.3       2,040                                       11    5                21.7       2,250                                       ______________________________________                                         .sup.5 Experiment E is a conventional copolymer and is a comparative          experiment.                                                              

These data show that the adhesion of ethylene-alkyl acrylate copolymerof this invention is substantially greater than the adhesion ofconventional ethylene-alkyl acrylate copolymers to another polymericsubstrate such as polyester.

Example 4 Adhesion of Copolymers of This Invention to Polypropylene

EMA copolymer was prepared by the conventional process as summarized inComparative Run A of Table 1 and had a MI of 20, a MA content of 20 wt.%, and a melting point of 181° F. A comparative two-layer cast filmconsisting of a 2.5-mil layer of polypropylene (Fina 3275) and a 2.5-millayer of this EMA copolymer prepared by the conventional process wereprepared on a Randcastle Mini-extruder.

EMA copolymer of this invention was prepared by the process assummarized in Run 3 of Table 1 and had a MI of 20, a MA content of 24wt. %, and a melting point of 185° F. A two-layer cast film of thisinvention consisting of a 2.5-mil layer of said polypropylene and a2.5-mil layer of this EMA copolymer was prepared on the RandcastleMini-extruder.

The adhesive strength of each of these films was determined using themethod of Example 3. The comparative film had an adhesive strength ofabout 815 gm/in., and the film of this invention had an adhesivestrength of about 1790 gm/in.

Example 5 Adhesion of Copolymers of This Invention to OrientedPolypropylene

EMA copolymer was prepared by the conventional process as summarized inComparative Runs A and B of Table 1. A comparative three-layer cast filmwas made on a pilot-plant extrusion line operating at 300 ft/min. Thefilm was made by extrusion coating a 0.75 mil substrate layer oforiented polypropylene (Mobil 410 LCM, available from Mobil ChemicalCo.) which was exposed to corona discharge at 300V with a 0.4-mil layerof this EMA copolymer and a 0.7-mil layer of an ethylene-acrylic acidionomer (Surlyn 1652, available from DuPont de Nemoir) simultaneously ata melt temperature of 580° F., such that the EMA copolymer layer wassandwiched between the oriented polypropylene layer and the ionomerlayer.

EMA copolymer of this invention was prepared by the process assummarized in Runs 3, 4 and 6 of Table 1. A three-layer cast film ofthis invention was prepared as above, substituting the EMA copolymer ofthis invention for the conventional EMA copolymer.

The adhesive strength of the oriented polypropylene and EMA copolymer ofeach of these films was determined using the method of Example 3. Thesemeasurements are summarized in Table 3.

Samples of these films were aged for 30 days at 80% relative humidityand at 72° F. The adhesive strengths of the films were determined usingthe method of Example 3. These measurements are also summarized in Table3.

Example 6 Adhesion of Copolymers of This Invention to Oriented Polyester

EMA copolymer was prepared by the conventional process as summarized inComparative Runs A and B of Table 1. A comparative three-layer cast filmwas made on a pilot-plant extrusion line operating at 300 ft/min. Thefilm was made by extrusion coating a 0.48-mil substrate layer oforiented polyester (Hoechst Hostaphan® 2DE1) which was exposed to coronadischarge at 300V with a 0.4-mil layer of this EMA copolymer and a0.7-mil layer of a low-density polyethylene (Chevron PE Grade 1017,available from Chevron Chemical Co.) simultaneously at a melttemperature of 600° F., such that the EMA copolymer layer was sandwichedbetween the oriented polypropylene layer and the ionomer layer.

EMA copolymer of this invention was prepared by the process assummarized in Runs 3, 4 and 6 of Table 1. A three-layer cast film ofthis invention was prepared as above, substituting the EMA copolymer ofthis invention for the conventional EMA copolymer.

The adhesive strength of the EMA copolymer to the oriented polyester foreach of these films was determined using the method of Example 3. Thesemeasurements are summarized in Table 3.

Samples of these films were aged for 30 days at 80% relative humidityand at 72° F. The adhesive strengths of the films were determined usingthe method of Example 3. These measurements are also summarized in Table3.

                  TABLE 3                                                         ______________________________________                                                  ADHESIVE STRENGTH, gm/in.                                                EMA                  OPP-EMA-      OPET-                                      COPOLYMER  OPP-      IONOMER OPET- EMA-PE                                     OF TABLE   EMA-      AGED 30 EMA-  AGED 30                               RUN  1          IONOMER.sup.7                                                                           DAYS    PE.sup.8                                                                            DAYS                                  ______________________________________                                        F.sup.6                                                                            B          310       270     140   70                                    12   4          380       270     320   90                                    G.sup.6                                                                            A          270       270     160   80                                    13   3          680       720     450   190                                   14   6          545       555     450   255                                   ______________________________________                                         .sup.6 Runs F and G are comparative examples.                                 .sup.7 OPP  oriented polypropylene.                                           .sup.8 OPET  oriented polyester; PE  polyethylene.                       

Example 7 Continuous Saponification of EMA Copolymer of This Inventionin an Extruder

A Werner & Pfleiderer corrosion resistant extruder was fitted with aliquid injection system. Downstream extruder equipment included a watercooling bath and a pelletizer.

The extruder was started, followed by the solid feeder and the liquidfeeder. The screws were maintained at 400 rpm. EMA copolymer of thisinvention, made by the method shown for Run 3 in Table 1 and containingabout 12 or 20 wt % methyl acrylate and having a melt index (MI) of 400to 630 gm/10 min., was fed into the extruder, and was reacted at atemperature between about 255° and 270° C. in the extruder with 50%aqueous sodium hydroxide solution. The saponification reaction startedin the injection zone and continued through the reaction zone. Excesswater and by-product methanol were removed in a devolatilization zone.The reaction product was extruded through a die as strands, cooled in awater bath and pelletized.

The following table summarize properties of the resultant ionomer.

                  TABLE 4                                                         ______________________________________                                                       IONOMER PROPERTIES                                                              MOL % OF MA                                                  EMA COPOLYMER    CONVERTED                                                    PROPERTIES       TO SODIUM   MELT-POINT                                       RUN   MA %    MI (g/10 min.)                                                                           ACRYLATE  TEMP. (°F.)                         ______________________________________                                        15    12      630        62        194                                        16    12      630        86        181                                        17    12      630        100       189                                        18    12      400        60        207                                        19    12      400        83        210                                        20    12       50        83        208                                        21    12      400        99        190                                        22    20      440        47        189                                        23    20      440        51        187                                        24    20      440        61        181                                        25    20      440        72        147                                        26    20      400        35        198                                        27    20      400        42        196                                        28    20      400        50        196                                        29    20      400        65        198                                        ______________________________________                                    

As the data above show, ionomers made from the ethylene-alkyl acrylatecopolymer of this invention have unexpectedly high melt-pointtemperatures, particularly those ionomers made from a copolymer having alow alkyl acrylate content. These ionomers are useful in applicationswhich require service temperatures at or near the boiling point ofwater. The superior adhesive strength of these ionomers over ionomersmade from conventional EAA copolymers permits their use in multi-layerconstructions such as food wrap and food bags.

The above-disclosed process for making copolymers of this invention isalso applicable to make ethylene-acrylic acid copolymers. Acrylic and/ormethacrylic acid is substituted in place of the alkyl acrylate above toproduce ethylene-acrylic acid copolymers having improved melt-pointtemperatures and/or improved adhesion to polymeric substrates such aspolyester or polypropylene over ethylene-acrylic acid copolymers made bythe conventional process disclosed above, substituting acrylic and/ormethacrylic acid for the alkyl acrylate of the conventional processabove.

We claim:
 1. A composition comprising a copolymer of ethylene and alkylacrylate, the copolymer having an adhesive strength to polyester atleast about 20% greater than the adhesive strength of a referencepolymer to polyester,wherein the copolymer contains from about 5 weightpercent to about 50 weight percent alkyl acrylate based on the totalweight of ethylene and alkyl acrylate in the copolymer, wherein thereference copolymer has the same amount and type of alkyl acrylate andethylene, and wherein the reference copolymer is made by dividing theethylene monomer and alkyl acrylate monomer equally among each reactorzone in a multi-zone reactor.
 2. The composition of claim 1 wherein thealkyl acrylate consists essentially of methyl acrylate, ethyl acrylate,butyl acrylate, or mixtures thereof.
 3. The composition of claim 2wherein the alkyl acrylate consists essentially of methyl acrylate,ethyl acrylate, butyl acrylate, or mixtures thereof.
 4. The compositionof claim 1 wherein the adhesive strength is at least 50 percent greaterthan the reference polymer.
 5. The composition of claim 4 wherein theadhesive strength is at least 100 percent greater than the referencepolymer.
 6. The composition according to claim 1 wherein the copolymerexhibits a melt-point temperature at least about 6 deg F. greater thanthe reference copolymer.
 7. The composition of claim 6 wherein theadhesive strength is at least 50 percent greater than the referencepolymer.
 8. The composition of claim 7 wherein the adhesive strength isat least 100 percent greater than the reference polymer.
 9. Thecomposition of claim 1 prepared by the process comprising:A) feedingoverall to a multi-zone reactor a total amount by weight, A, of alkylacrylate and a total amount by weight, E, of ethylene; B) reacting in afirst reaction zone of the reactor a portion by weight, A₁, of the alkylacrylate and a portion by weight, E₁, of the ethylene, such that A₁ /E₁is at least about 10% greater than A/E; C) reacting any remainingportions of ethylene and alkyl acrylate in a subsequent reaction zone orzones.
 10. The composition according to claim 9 wherein A₁ /E₁ is atleast about 20% greater than A/E.
 11. The composition according to claim10 wherein A₁ /E₁ is at least about 25% greater than A/E.
 12. Thecomposition according to claim 11 wherein A₁ /E₁ is at least about 50%greater than A/E.
 13. The composition according to claim 12 wherein A₁/E₁ is at least about 100% greater than A/E.
 14. The compositionaccording to claim 9 wherein E₁ /E is between about 0.10 and 0.90. 15.The composition according to claim 9 wherein A is about 10 to about 40weight percent.
 16. The composition according to claim 15 wherein A isabout 15 to about 40 weight percent.
 17. The composition according toclaim 9 wherein the reactor is a stirred autoclave reactor.
 18. Acomposition comprising a copolymer of ethylene and alkyl acrylate, thecopolymer having a melt-point temperature at least about 6 deg F.greater than a reference copolymer,wherein the copolymer is prepared bythe method comprising:A) feeding overall to a multi-zone reactor a totalamount by weight, A, of alkyl acrylate and a total amount by weight, E,of ethylene, wherein A is about 5 weight percent to about 50 weightpercent of the total copolymer; B) reacting in a first reaction zone ofthe reactor a portion by weight, A₁, of the alkyl acrylate and a portionby weight, E₁, of the ethylene, such that A₁ /E₁ is at least about 10%greater than A/E; and C) reacting any remaining portions of ethylene andalkyl acrylate in a subsequent reaction zone or zones; wherein thereference copolymer has the same amount and type of alkyl acrylate andethylene, and wherein the reference copolymer is made by dividing theethylene monomer and alkyl acrylate monomer equally among each reactorzone in a multi-zone reactor.
 19. The composition according to claim 18wherein the copolymer is an ethylene-methyl acrylate copolymer having anaverage melt-point temperature of equal to or greater than the valueobtained from the formula:

    Temperature (deg F.)=248-3.1Y

wherein Y is the weight percent methyl acrylate.
 20. The compositionaccording to claim 19 wherein the methyl acrylate content is equal to orgreater than 15 weight percent.
 21. The composition of claim 18 whereinthe copolymer is an ethylene-butyl acrylate copolymer having an averagemelt-point temperature of equal to or greater than the value obtainedfrom the formula:

    Temperature (deg F.)=240-2.3Z

wherein Z is the weight percent butyl acrylate.
 22. The compositionaccording to claim 21 wherein the butyl acrylate content is equal to orgreater than 15 weight percent.
 23. The composition according to claim18 wherein A₁ /E₁ is at least about 20% greater than A/E.
 24. Thecomposition according to claim 23 wherein A₁ /E₁ is at least about 25%greater than A/E.
 25. The composition according to claim 24 wherein A₁/E₁ is at least about 50% greater than A/E.
 26. The compositionaccording to claim 25 wherein A₁ /E₁ is at least about 100% greater thanA/E.
 27. The composition according to claim 26 wherein E₁ /E is betweenabout 0.10 and 0.90.
 28. The composition according to claim 18 wherein Ais about 10 to about 40 weight percent.
 29. The composition according toclaim 28 wherein A is about 15 to about 40 weight percent.
 30. Thecomposition according to claim 18 wherein the reactor is a stirredautoclave reactor.